1. Field of the Invention
The invention relates generally to a resettable shutter having apparatus that normally limits the duration of an exposure to correspond to a predetermined scene brightness and apparatus to selectively disable the limiting apparatus to provide an exposure of extended duration that corresponds to actual scene brightness, and more particularly to apparatus that re-enables the limiting apparatus after disablement each time the shutter is reset.
2. Description of the Prior Art
Because of the difficulty in hand holding a camera steady throughout a long exposure, the duration of an automatically controlled exposure provided by some cameras is often limited to a maximum interval related to the longest time that the camera can be effectively held steady by hand. Various apparatus have been used to control the duration of the exposure while limiting its duration to a predetermined maximum. One such apparatus uses a primary timing device whose output is related to actual scene brightness, that is operated concurrently with an auxiliary timing device whose output is independent of scene brightness. The outputs of the timing devices are compared and if the output of the primary timing device has not terminated the exposure prior to the exposure reaching the predetermined maximum interval, the output of the auxiliary timing device terminates the exposure. Commonly assigned, copending U.S. application Ser. No. 409,228 filed Sept. 13, 1973 in the name of Robert V. Alessi, discloses such a timing device, in which a primary timing circuit is responsive to scene brightness and an auxiliary timing circuit, operated independently of light and concurrently with the light-responsive timing circuit, limits the duration of the exposure. This device includes a switch that is actuatable to disable the auxiliary timing circuit so that the light-responsive timing circuit may provide an extended exposure that is related to actual scene brightness. However, in such prior art devices, the operator must remember to reset the switch to effect an exposure of limited duration after the extended duration exposure feature has been used. To forget to re-enable the limited-duration exposure, often results in blurred photographs.